Background technology
The output voltage of photovoltaic cell and output current change along with the variation of the factors such as intensity of illumination, battery temperature and load, and the position of Maximum Power Output is unfixed.Under given conditions, photovoltaic cell output nonlinear and have unique maximum power point.
Conventional maximum power point tracing method has constant voltage process (CV), disturbance observation (P & O), increment conductance method (INC), fuzzy control etc., also has some improving one's methods based on practical problem.That constant voltage process is controlled is simple, be easy to realize, but bad adaptability, precision are low.Disturbance observation is controlled simple, convenient realization, in step-length hour, but precision is high, to shake little tracking velocity too slow; When step-length is larger, tracking velocity is fast, has but reduced precision, adds according to system concussion.It is better that increment conductance method is controlled effect, but control algolithm is complicated, to system accuracy, require high.Fuzzy control flexibly, comprehensive, compatibility is good, but causes system control precision to reduce and dynamic property decline.
Summary of the invention
To the object of the invention is in order addressing the above problem, to propose a kind of maximum power point of photovoltaic power generation system tracking, can follow the trail of fast the maximum power point of photovoltaic cell, and system is shaken the energy loss of bringing near maximum power point while reducing stable state.
A maximum power point of photovoltaic power generation system tracking, comprises the following steps:
Step 1: sampling photovoltaic battery open circuit voltage V
oc, the voltage V while exporting according to maximum power point
mwith open circuit voltage V
ocmeet V
m=mV
oc, choose the interval [m that comprises maximum power point
1v
oc, m
2v
oc] as between initial iterative region, wherein: V
ocfor open circuit voltage; V
mvoltage while exporting for maximum power point; M, m
1, m
2constant coefficients, span: 0≤m
1< m < m
2≤ 1.
Step 2: according to formula
calculate iterations n.Wherein: n is iterations; T is search precision, is more than or equal to the minimum precision that system allows.
Step 3: represent a=m when initial between iterative region with [a, b]
1v
oc, b=m
2v
oc.K is iterations, meets 0≤k≤n.According to formula
obtain the mid point between the k time iterative region, measuring distance mid point V
z(k) charging current of left and right sides ε electrical voltage point.Be V
l(k)=V
z(k)-ε and V
r(k)=V
z(k) the charging current I that+ε is ordered
l(k), I
r(k) value, according to formula P=V*I, calculates respectively this power P of 2
l(k), P
r(k).
Wherein: V
z(k) be the k time iteration voltage range midrange; ε is greater than zero real number; V
l(k) be mid point V between distance regions
z(k) magnitude of voltage of left side ε; V
r(k) be interval mid point V
z(k) magnitude of voltage of right side ε; I
l(k) be V
l(k) electrical voltage point is corresponding charging current value, I
r(k) be V
r(k) charging current value corresponding to electrical voltage point; P
l(k), P
r(k) be respectively electrical voltage point V
l(k), V
r(k) corresponding performance number.
Step 4: judgement P
land P (k)
r(k) size, if P
l(k) > P
r(k), change between iterative region, between new iterative region, a remains unchanged, by V
r(k) assignment, to b, becomes a=a, b=V
r(k); Otherwise, between new iterative region by V
l(k) assignment is to a, and b remains unchanged.Become a=V
l(k), b=b.
Step 5: judge whether k reaches iterations n, if do not have, returns to step 3, carries out new round iteration; If reach iterations n, choose mid point between final iterative region as maximum power electrical voltage point V
m, measure corresponding charging current I
m, according to formula P=V*I, calculate maximum power P
m.
The invention has the advantages that:
The method of the invention rapid dynamic response speed, the maximum power point of tracking photovoltaic array, has reduced the energy loss of system in maximum power point vibration exactly, has improved the delivery efficiency of photovoltaic cell.
Embodiment
Below in conjunction with drawings and Examples, the present invention is described in further detail.
The present invention is a kind of maximum power point of photovoltaic power generation system tracking, and flow process as shown in Figure 1, comprises the following steps:
Step 1: sampling photovoltaic battery open circuit voltage V
oc, the voltage V while exporting according to maximum power point
mwith open circuit voltage V
ocmeet V
m=mV
oc, choose the interval [m that comprises maximum power point
1v
oc, m
2v
oc] as between initial iterative region, wherein: V
ocfor open circuit voltage; V
mvoltage while exporting for maximum power point; M, m
1, m
2constant coefficients, span: 0≤m
1< m < m
2≤ 1.
Step 2: according to formula
calculate iterations n.Wherein: n is iterations; T is search precision, is more than or equal to the minimum precision that system allows.
Step 3: represent a=m when initial between iterative region with [a, b]
1v
oc, b=m
2v
oc.K is iterations, meets 0≤k≤n.According to formula
obtain the mid point between the k time iterative region, measuring distance mid point V
z(k) charging current of left and right sides ε electrical voltage point.Be V
l(k)=V
z(k)-ε and V
r(k)=V
z(k) the charging current I that+ε is ordered
l(k), I
r(k) value, according to formula P=V*I, calculates respectively this power P of 2
l(k), P
r(k).
Wherein: V
z(k) be the k time iteration voltage range midrange; ε is greater than zero real number; V
l(k) be mid point V between distance regions
z(k) magnitude of voltage of left side ε; V
r(k) be interval mid point V
z(k) magnitude of voltage of right side ε; I
l(k) be V
l(k) electrical voltage point is corresponding charging current value, I
r(k) be V
r(k) charging current value corresponding to electrical voltage point; P
l(k), P
r(k) be respectively electrical voltage point V
r(k), V
r(k) corresponding performance number.
Step 4: judgement P
land P (k)
r(k) size, if P
l(k) > P
r(k), change between iterative region, between new iterative region, a remains unchanged, by V
r(k) assignment, to b, becomes a=a, b=V
r(k); Otherwise, between new iterative region by V
l(k) assignment is to a, and b remains unchanged.Become a=V
l(k), b=b.
Step 5: judge whether k reaches iterations n, if do not have, returns to step 3, carries out new round iteration; If reach iterations n, choose mid point between final iterative region as maximum power electrical voltage point V
m, measure corresponding charging current I
m, according to formula P=V*I, calculate maximum power P
m.
Embodiment: the present invention chooses m
1be 0.6, m
2be 0.9,, maximum power point voltage is at interval [0.6V
oc, 0.9V
oc] in.As shown in Figure 2, interval midrange is
choose ε=0.01, near midrange, left side magnitude of voltage is 0.75V
oc-0.01, right side magnitude of voltage is 0.75V
oc+ 0.01.If V
ocget 21.75V, between interval [13.05V, 19.575V] original area as search.Choose error t=0.1, obtain iterations:
n=7
Iterations is 1 o'clock, interval mid point V
z=16.3125V, so disturbance voltage V
1=16.3025V, V
2=16.3225V.Judgement P (V
1) and P (V
2) magnitude relationship, if P (V
1) > P (V
2), interval becomes
if P is (V
1) < P (V
2), interval becomes [16.3025V, 19.575V].Between Zai Yi new district, between iterative region, repeat above step, until iterations arrives 7, meet required precision.
The present invention follows the tracks of that number of times is few, speed is fast, steady-state behaviour system improves, and has improved the utilization ratio of photovoltaic cell.